This proposal principally concerns the organization of the accessory optic system and its relation to optokinetic nystagmus (OKN) and the vestibulo-ocular reflex (VOR). On the basis of neurophysiological evidence suggesting that the accessory optic system (nucleus of the basal optic root, nBOR) of birds transforms retinal signals into signals conveying information about whole-field retinal slip in a vestibular coordinate system, we propose to study in detail this neural transformation, using single-unit recording techniques. We will also study, both with recording and lesioning techniques, the nuclei to which the accessory optic sytem and pretectum project, in particular the medial and lateral pontine nuclei and the interstitial nucleus of Cajal, in the hope of better understanding the organization of the neural structures that process retinal slip information. In addition, we propose experiments to attempt to distinguish the functions of the accessory optic system and the pretectum. We have found that under appropriate conditions, the OKN behavior of chickens exhibits substantial asymmetries in gain to stimulus movement in different directions that suggest that the optokinetic system is organized with respect to the planes of the semicircular canals, presumably to facilitate combining visual and vestibular information about head motion. We propose to test whether this is a general feature of the optolinetic system by studies on directional asymmetries of OKN in humans, as well as in birds. Chickens show very rapid adaptive modification of their VOR gain and phase. We propose studies directed at understanding how the brain uses retinal slip signals to form an error signal that guides these adaptive modifications. Studies on the ontogeny of nBOR responses, OKN, and VOR are also planned because of evidence from 2-deoxylgucose studies of intersting developmental changes early in life.